The blaze at Bundaleer North has been burning since Wednesday afternoon and has already destroyed about 2300 hectares of forest and scrub.
About 200 firefighters have been battling the fire along with three fixed-wing water bombers.
Country Fire Service state co-ordinator Mark Thomason said crews were making a concerted effort to establish control lines before the wind shift.
‘The expected wind change will potentially push the fire in an easterly direction towards some farming communities, which is of concern,’ Mr Thomason said.
‘Our crews have been working diligently on this fire since late last night and we’re hoping that their efforts will pay off.’
The blaze has closed a number of roads in the mid-north while smoke has extended beyond the Clare and Gilbert Valley region, reaching towns further south including Port Wakefield and Mallala.
The fire came as most of SA endured extremely hot conditions, with Adelaide posting a top temperature of 43 degrees.
Some regional centres experienced even worse heat, with the mercury reaching 46.4 degrees at Port Augusta.
A cool change was expected across the state later on Thursday with Adelaide’s forecast top for Friday a much more comfortable 27 degrees.
Source: Sky News Australia